This invention relates to articles, particularly brass articles, coated with a multi-layered decorative and protective coating having the appearance or color of stainless steel.
It is currently the practice with various brass articles such as faucets, faucet escutcheons, door knobs, door handles, door escutcheons and the like to first buff and polish the surface of the article to a high gloss and to then apply a protective organic coating, such as one comprised of acrylics, urethanes, epoxies and the like, onto this polished surface. This system has the drawback that the buffing and polishing operation, particularly if the article is of a complex shape, is labor intensive. Also, the known organic coatings are not always as durable as desired, and are susceptible to attack by acids. It would, therefore, be quite advantageous if brass articles, or indeed other articles, either plastic, ceramic, or metallic, could be provided with a coating which provided the article with a decorative appearance as well as providing wear resistance, abrasion resistance and corrosion resistance. It is known in the art that a multi-layered coating can be applied to an article which provides a decorative appearance as well as providing wear resistance, abrasion resistance and corrosion resistance. This multi-layer coating includes a decorative and protective color layer of a refractory metal nitride such as a zirconium nitride or a titanium nitride. This color layer, when it is zirconium nitride, provides a brass color, and when it is titanium nitride provides a gold color.
U.S. Pat. Nos. 5,922,478; 6,033,790 and 5,654,108, inter alia, describe a coating which provides an article with a decorative color, such as polished brass, and also provides wear resistance, abrasion resistance and corrosion resistance. It would be very advantageous if a coating could be provided which provided substantially the same properties as the coatings containing zirconium nitride or titanium nitride but instead of being brass colored or gold colored was stainless steel colored. The present invention provides such a coating.
The present invention is directed to an article such as a plastic, ceramic or metallic article having a decorative and protective multi-layer coating deposited on at least a portion of its surface. More particularly, it is directed to an article or substrate, particularly a metallic article such as aluminum, brass or zinc, having deposited on its surface multiple superposed layers of certain specific types of materials. The coating is decorative and also provides corrosion resistance, wear resistance and abrasion resistance. The coating provides the appearance of stainless steel, i.e. has a stainless steel color tone. Thus, an article surface having the coating thereon simulates a stainless steel surface.
The article first has deposited on its surface a polymeric basecoat layer. On top of the polymeric basecoat layer is then deposited, by vapor deposition such as physical vapor deposition, a sandwich or stack layer. More particularly, a first layer deposited directly on the surface of the substrate is comprised of a polymer. Disposed over the polymeric layer is a vapor deposited protective sandwich or stack layer comprised of layers containing a refractory metal or refractory metal alloy alternating with layers containing a refractory metal nitrogen and oxygen containing compound or a refractory metal alloy nitrogen and oxygen containing compound. Over the sandwich or stack layer is vapor deposited at relatively low pressure a color layer comprised of a refractory metal nitrogen and oxygen containing compound or a refractory metal alloy nitrogen and oxygen containing compound. The refractory metal nitrogen and oxygen containing compounds or refractory metal alloy nitrogen and oxygen containing compounds are the reaction products of a refractory metal or refractory metal alloy, oxygen and nitrogen, wherein the nitrogen and oxygen content is low, i.e., substoichiometric. The total nitrogen and oxygen content of these refractory metal nitrogen and oxygen containing compounds or refractory metal alloy nitrogen and oxygen containing compound is from about 4 to about 32 atomic percent, preferably from about 5 to about 28 atomic percent, with the nitrogen content being at least about 3 atomic percent, preferably at least about 4 atomic percent. The protective color layer is deposited at relatively low pressures in the vacuum coating chamber. These relatively low pressures are generally below about 8 millitorr, preferably below about 5 millitorr, and more preferably below about 3 millitorr. This low pressure deposition provides a protective color layer exhibiting improved mechanical properties, particularly improved abrasion resistance, and improved corrosion resistance.
The lightly nitrided and oxidized color layer is mainly comprised of amorphous metallic refractory metal with textured metal nitride phase. For example, zirconium nitride oriented in (111) plane and smaller than 50 nm in grain size, or metallic zirconium oriented in (112) plane and smaller than 80 nm, depending on the proportion of oxygen in total gas flow. Such types of structures are produced at relatively low processing pressures, ranging from 1 to 5 millitorr. The color of the coating can be adjusted slightly bluish or yellowish by increasing or decreasing the oxygen to nitrogen ratio.